Iron or steel articles having a surface layer of austenitic manganese steel ("Hadfield" manganese steel) are well known in the metallurgical art, see, e.g., Avery, "Austenitic Manganese Steel," ASM Metals Handbook, 8th Edition, Vol. 1, p. 6 (1977), and Kornmann et al., "Manganese Diffusion Coating of Steels," Metals Technology, p. 218, (April, 1977). Hadfield manganese steel is characterized by an ability to undergo work hardening and by a substantial resistance to impact and abrasion. However, a drawback to the use of Hadfield manganese steel is its susceptibility to plastic deformation under load.
Powder metallurgy techniques have been used to make iron and steel articles containing manganese as an alloying ingredient, see, e.g., U.S. Pat. Nos. 3,459,547, 3,708,281, 4,071,354, 4,092,223, Salak, "Sintered Manganese Steels, Parts I and II," Powder Metallurgy International, 12, 1 and 2 (1980), and Schwarzkopf, Iron Steel Inst. Special Report No. 58, pp. 55-58 (1956). The manganese-containing articles described in these references are compacts made by pressing methods, and such articles therefore do not have uniform density and homogeneous composition. Also, the articles of these references generally have a low manganese content (for example, less than one percent by weight of the final article in many cases) or have a fully homogeneous manganese composition, or have both low manganese content and homogeneous manganese composition. In addition, one of these references (viz., U.S. Pat. No. 4,071,354) reported that manganese diffusion into iron occurred very rapidly, and much more rapidly than diffusion of metals such as molybdenum, nickel, and chromium into iron.
A need exists for a process and articles which provide precision molded articles (such as die cavities) with abrasion resistance and impact resistance comparable to Hadfield manganese steel, but with greater resistance to plastic deformation than that exhibited by Hadfield manganese steel.